1. Field of the Invention
This invention relates to a semiconductor device and a control method thereof.
2. Description of the Related Art
FIG. 1 is a view showing a circuit configuration of a conventional non-volatile semiconductor memory device at the time of programming. As shown in FIG. 1, a non-volatile semiconductor memory device 20 includes a program voltage generating circuit 1, a program voltage supply circuit 2, a data in buffer circuit (dinbuf_be) 3, a Y decoder (ysel) 4, and a memory cell 5. The memory cell 5 is a flash memory having a floating gate or a nitride film, serving as a charge accumulation layer. A high voltage is applied to a drain terminal of the memory cell 5 to inject hot carriers into the charge accumulation layer at the time of programming. A high program voltage VPROG in the non-volatile semiconductor memory device 20 is a voltage in which the voltage generated by the program voltage generating circuit 1 is regulated to a constant voltage, and is supplied to a common data bus line connected to a bit line BL via the program voltage supply circuit 2.
The semiconductor memory device described in Japanese Patent Application Publication No. 2001-15716 (hereinafter referred to as Document 1) controls a current supplied to the drain of the memory cell with a constant current element that controls the current not to exceed a given value, when a hot electron is injected into the floating gate, and is capable of suppressing a program period at minimum by controlling the gate voltage to be supplied to the control gate output from a given comparator.
However, the program voltage generating circuit (drain pump) 1 that supplies the current to the drain of the memory cell 5 needs a current supply capacity equal to or greater than (the number of bits to be programmed)×(a program current for every bit). When multiple bits are programmed simultaneously, a large amount of current flows through the memory cell 5 at the time of programming. There arises the problem in that the output voltage of the drain pump is decreased and the multiple bits cannot be programmed simultaneously. In addition, the current supply capacity can be enhanced by increasing the number of the program voltage generating circuits 1, yet this causes another problem of enlarging the circuitry scale. Further, there is further another problem in that the technique described in Document 1 cannot control the gate voltage correctly.